Biomagnification of Pollutants
- Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants with ascending trophic level through a food chain
- Not to be confused with bioaccumulation, which is the build-up of pollutants within an organism, or within a single trophic level
- As pollutants are passed up the food chain from one trophic level to the next, they can become more concentrated due to the decrease in total biomass of organisms at higher trophic levels
- I.e. the smaller organisms at the bottom of the food chain will each consume a small volume of pollutant, and then the organisms at the top of the food chain will consume many smaller organisms and receive a much larger dose of pollutant
Biomagnification of DDT
- Toxins such as DDT (dichlorodiphenyltrichloroethane) are persistent pollutants that can enter food chains
- DDT was a widely used insecticide in the mid-20th century that was found to have harmful effects on top predators such as birds of prey
- When DDT was sprayed on crops, it would leach into waterways and eventually enter freshwater and marine ecosystems
- DDT would then enter food chains via plankton and accumulate in the bodies of fish
- These fish would then be eaten by birds, which would accumulate higher concentrations of DDT
- Because DDT is persistent and does not break down easily, it can continue to accumulate in the bodies of animals at higher trophic levels, leading to harmful effects such as thinning of eggshells and reduced reproductive success
- The thin eggshells could not withstand the weight of the parent bird during incubation, so the eggs would break and fewer young birds would hatch
- Over time this resulted in reduced bird populations
- DDT has now been banned worldwide, with the exception of its use in areas where it is essential in dealing with mosquitos that transmit malaria
Biomagnification of DDT diagram
Through the process of biomagnification, the concentration of DDT in the tissues of organisms increases at successively higher trophic levels in a food chain
Biomagnification of mercury
- Mercury is another example of a pollutant that can accumulate through food chains
- Mercury is released into the environment through activities such as coal-fired power plants and gold mining
- Once in the environment, mercury can be converted by microorganisms into a highly toxic form called methyl mercury, which can accumulate in the bodies of fish
- As larger fish eat smaller fish, the concentration of methyl mercury within the tissues of these fish increases, leading to potential harm for humans who eat large predatory fish such as tuna or swordfish